An essential part of semiconductor integrated circuit manufacture resides in the placing of the integrated circuit chip into a package so that the chip can be conveniently contacted electrically as well as mounted in a physically secure manner. The chip itself is mounted on a lead frame which has a plurality of fingers for electrical connections and a paddle for physical support. The paddle is connected physically to an external mounting frame by paddle support arms. Electrical contacts are made through wires bonded to the fingers and to the paddle.
Although the package could be assembled using a lead frame in which the paddle remains in the same plane as do the fingers, it has often been found desirable to assemble a package using a lead frame in which the paddle has been depressed, i.e., made lower, with respect to the external mounting frame and fingers. It has been found that this configuration reduces the number of edge shorts between the electrical contact wires and the chip. It also allows a balanced flow condition during molding. As will be readily appreciated by those skilled in the art, the depressed positioning will necessarily lead to a physical deformation of the paddle support arms during the forming process because the lead frame is initially a flat metal piece. The deformation will generally be in the form of a necking down, i.e., a constriction of paddle support arms in the transverse axial direction.
As feature sizes in integrated circuits continue to decrease and the scale of integration continues to increase, package designers must make more interconnects in an amount of space that is, at best, equal to that previously available. The only expedient way this may be accomplished is to decrease the width of the fingers and paddle support arms to permit placement of more fingers in either the same or a smaller area. Consequently, the combined effect of the constriction and decreased feature size may lead to problems such as loss of physical integrity and distortion of the paddle support arms. If these arms are also used for electrical connections, there may be undesirable changes in the electrical characteristics as well.